The proportionate width and
height of doors may be settled, if they are Doric, in the Doric manner,
and if Ionic, in the Ionic manner, according to the rules of symmetry
which have been given about portals in the fourth book. In the
roof-opening let an aperture be left with a breadth of not less than
one fourth nor more than one third the width of the atrium, and with a
length proportionate to that of the atrium.

[Illustration: _Photo. Sommer_

THE PERISTYLE OF THE HOUSE OF THE VETTII AT POMPEII]

7. Peristyles, lying athwart, should be one third longer than they are
deep, and their columns as high as the colonnades are wide.
Intercolumniations of peristyles should be not less than three nor more
than four times the thickness of the columns. If the columns of the
peristyle are to be made in the Doric style, take the modules which I
have given in the fourth book, on the Doric order, and arrange the
columns with reference to these modules and to the scheme of the
triglyphs.

[Illustration: _From Durm_

PLAN OF THE HOUSE OF THE VETTII, POMPEII]

8. Dining rooms ought to be twice as long as they are wide. The height
of all oblong rooms should be calculated by adding together their
measured length and width, taking one half of this total, and using the
result for the height. But in the case of exedrae or square oeci, let
the height be brought up to one and one half times the width. Picture
galleries, like exedrae, should be constructed of generous dimensions.
Corinthian and tetrastyle oeci, as well as those termed Egyptian, should
have the same symmetrical proportions in width and length as the dining
rooms described above, but, since they have columns in them, their
dimensions should be ampler.

9. The following will be the distinction between Corinthian and Egyptian
oeci: the Corinthian have single tiers of columns, set either on a
podium or on the ground, with architraves over them and coronae either
of woodwork or of stucco, and carved vaulted ceilings above the coronae.
In the Egyptian there are architraves over the columns, and joists laid
thereon from the architraves to the surrounding walls, with a floor in
the upper story to allow of walking round under the open sky. Then,
above the architrave and perpendicularly over the lower tier of columns,
columns one fourth smaller should be imposed. Above their architraves
and ornaments are decorated ceilings, and the upper columns have windows
set in between them.